linux-kernel - [tip:x86/asm] x86/insn-eval: Handle 32-bit address encodings in virtual-8086 mode

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Date:   Wed, 8 Nov 2017 02:59:03 -0800
From:   tip-bot for Ricardo Neri <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     adam.buchbinder@...il.com, dvyukov@...gle.com, tony.luck@...el.com,
        pbonzini@...hat.com, peterz@...radead.org, hpa@...or.com,
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        jpoimboe@...hat.com, linux-kernel@...r.kernel.org,
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        mst@...hat.com, adrian.hunter@...el.com,
        paul.gortmaker@...driver.com, bp@...e.de
Subject: [tip:x86/asm] x86/insn-eval: Handle 32-bit address encodings in
 virtual-8086 mode

Commit-ID:  86cc35109029b7f1b195cef6c74654bad95e81af
Gitweb:     https://git.kernel.org/tip/86cc35109029b7f1b195cef6c74654bad95e81af
Author:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
AuthorDate: Sun, 5 Nov 2017 18:27:49 -0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 8 Nov 2017 11:16:20 +0100

x86/insn-eval: Handle 32-bit address encodings in virtual-8086 mode

It is possible to utilize 32-bit address encodings in virtual-8086 mode via
an address override instruction prefix. However, the range of the
effective address is still limited to [0x-0xffff]. In such a case, return
error.

Also, linear addresses in virtual-8086 mode are limited to 20 bits. Enforce
such limit by truncating the most significant bytes of the computed linear
address.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Adam Buchbinder <adam.buchbinder@...il.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Chen Yucong <slaoub@...il.com>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Colin Ian King <colin.king@...onical.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Huang Rui <ray.huang@....com>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: Jonathan Corbet <corbet@....net>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Lorenzo Stoakes <lstoakes@...il.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Qiaowei Ren <qiaowei.ren@...el.com>
Cc: Ravi V. Shankar <ravi.v.shankar@...el.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Thomas Garnier <thgarnie@...gle.com>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: ricardo.neri@...el.com
Link: http://lkml.kernel.org/r/1509935277-22138-5-git-send-email-ricardo.neri-calderon@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/lib/insn-eval.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 1ac3973..ef102db 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -1042,12 +1042,23 @@ static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs)
 		goto out;
 
 	/*
+	 * Even though 32-bit address encodings are allowed in virtual-8086
+	 * mode, the address range is still limited to [0x-0xffff].
+	 */
+	if (v8086_mode(regs) && (eff_addr & ~0xffff))
+		goto out;
+
+	/*
 	 * Data type long could be 64 bits in size. Ensure that our 32-bit
 	 * effective address is not sign-extended when computing the linear
 	 * address.
 	 */
 	linear_addr = (unsigned long)(eff_addr & 0xffffffff) + seg_base;
 
+	/* Limit linear address to 20 bits */
+	if (v8086_mode(regs))
+		linear_addr &= 0xfffff;
+
 out:
 	return (void __user *)linear_addr;
 }